In a report published Wednesday evening, the Wall Street Journal outlined an alleged Department of Justice project that uses fake cellphone towers mounted on small planes to surveil thousands of cellphones across the entire population of the United States. Almost 48 hours later, the DOJ still hasn't commented or responded on the validity of the article. It would neither confirm nor deny information to the Journal before publication, and has repeatedly refused to comment since.

The Journal reports that the DoJ uses the system to search for suspects “including fugitives and drug dealers,” but collects data from innocent bystanders in the process as well. And the Journal notes that even smartphones protected by standard encryption, like the iPhone 6, are still vulnerable. The project is apparently run by the Technical Operations Group of the U.S. Marshals.

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Essentially the program outfits Cessna airplanes with devices sometimes called “dirtboxes” that act like cellphone towers. The phony transmitters trick phones into seamlessly picking up their signal and revealing unique registration data. Sources told the Journal that data collected in a given area is processed right away to identify people on the ground, and is then “let go” if the system doesn't find anyone of interest, but it's unclear what exactly that means.

The device can briefly interrupt calls on certain phones. Authorities have tried to minimize the potential for harm, including modifying the software to ensure the fake tower doesn’t interrupt anyone calling 911 for emergency help, one person familiar with the matter said.

The program cuts out phone companies as an intermediary in searching for suspects. Rather than asking a company for cell-tower information to help locate a suspect, which law enforcement has criticized as slow and inaccurate, the government can now get that information itself. People familiar with the program say they do get court orders to search for phones, but it isn’t clear if those orders describe the methods used because the orders are sealed.

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As Wired points out, the devices used as phony cell towers seem like they may be IMSI catchers, otherwise known as stingrays, that have been used by law enforcement and intelligence-gathering agencies for years to spy on cellphones.

And Dave Maass, a researcher at the Electronic Frontier Foundation, has found evidence of other agencies using dirtboxes.

Since the DoJ hasn't commented yet, it’s not entirely clear what the goal of the program is or how it has been implemented ... if it exists ... which it seems like it does because the DOJ isn’t flat out denying it. But the Journal report is fairly comprehensive, and seems to reveal yet another way that government agencies are surveilling Americans.